WO1991014018A1

WO1991014018A1 - Electrolytic apparatus for protection against corrosion of a freshwater piping system

Info

Publication number: WO1991014018A1
Application number: PCT/DK1991/000076
Authority: WO
Inventors: Hans SØRENSEN
Original assignee: I Krueger As
Current assignee: I Krueger As
Priority date: 1990-03-12
Filing date: 1991-03-12
Publication date: 1991-09-19
Anticipated expiration: 1992-09-12
Also published as: DK64290D0; DE4190516T1; AU7469591A; DK64290A; DE4190516C2; DK169197B1

Abstract

An electrolytic apparatus for protection against corrosion of a freshwater piping system connected to a water tank (1) has at least two electrodes (2, 3) arranged in the tank (1) and a control unit (4) with a source of current. The electrodes (2, 3) are of aluminium and connected to the source of current by means of a pole changer (5) in such a manner that the electrodes (2, 3) alternately function as anode and cathode. As a result, an electrolytic apparatus which substantially prevents the bacteria from propagating in the tank (1) is obtained, which at the same time ensures protection against corrosion of the freshwater piping system. The tank (1) is preferably provided with a conical, lower end plate (16) which facilitates the flushing out of the calcium and sludge.

Description

Title: Electrolytic apparatus for protection against corrosion of a freshwater piping system

Technical Field

The invention relates to an electrolytic apparatus for protection against corrosion of a fresh water piping system connected to a water tank, said electrolytic apparatus having at least two electrodes which are placed in the tank and a control unit with a source of current.

Background Art

Danish patent specification No. 130,019 disloses an e.ϊec- trolytic apparatus for electrolytic water treatment in a fresh water system with an associated water tank, which electrolytic apparatus has a source of current between a cathode formed by the tank and two anodes arranged in the tank. During the use of such apparatus, large quantities of sludge and calcium will conventionally be accumulated as depositions on the walls and bottom of the water tank.

The depositions may provide favourable conditions of growth to bacteria and therefore the presence of an excessive amount of bacteria has presented a problem in known ap- paratuses .

Disclosure of Invention

The object of the invention is to provide an electrolytic apparatus of the above type which substantially prevents bacteria from propagating in the apparatus and which at the same time ensures protection against corrosion of the fresh water piping system.

The electrolytic apparatus according to the invention is characterised in that the electrodes are of aluminium and^* connected to the source of current through a pole changer in such a manner that the electrodes alternately function as anode and cathode. As a consequence of said construction, the electrodes and the water between said electrodes may be viewed as an isolated electrolytic cell connected to an alternating supply of current. As a result, during the use of the electrolytic apparatus, the calcareous deposition may be restricted to a predetermined area, that is to the electrode which serves as cathode during the periode of time in question. When the pole is changed by means of the pole changer the calcium depo¬ sitions formed on the cathode are loosened and settle, whereupon they are flushed out. Compared to the known electrolytic apparatuses, a considerable reduction of the amount of sludge and calcium present in the tank is thereby obtained. As a result, the bacteria are provided with less favourable growth conditions resulting in a lower germination index. Furthermore, during the use of the electrolytic apparatus the electrodes each gradually dissolve during the time in which they serve as anodes and the dissolved aluminium forms aluminium hydroxide. The aluminium hydroxide has a favourable effect in that together with liberated calcium carbonate it covers the inner surfaces of the freshwater piping system with a corrosion inhibiting layer.

According to the invention, the electrodes may be two substantially identical, soluble electrodes. A simple and inexpensive embodiment of the electrolytic apparatus is thereby obtained.

Moreover, according to the invention at least one soluble, additional anode may be arranged in the tank, said anode being of aluminium, zink or a similar material and having a separate supply of current from the control unit. The soluble, additional anode provides a cathodic protection against corrosion of the tank itself.

Further according to the invention one eletrode may furthermore have a separate supply of current from the control unit. As a result, a cathodic protection against corrosion of the tank per se is obtained without the use of an additional anode, whereby a particularly simple embodiment of the electrolytic apparatus is obtained.

In addtion, according to the invention the tank may be provided with a conical, lower end plate, the lower top point of which is provided with an outlet valve. By means of the gravitation, a large proportion of the precipitated calcium is thereby collected in the conical top point of the end plate, that is just above the outlet valve, thereby facilitating the flushing out of the calcium.

Finally, according to the invention the electrolytic apparatus may be structured in such a manner that at the bottom the tank is provided with a rinsing ring extending close to the skirt of the tank, said rinsing ring being provided with a number of rinsing nozzles, and that an outlet valve is placed in the lower end plate of the tank. Thereby the calcium depositions loosened from the elec- trodes by means of the pole changing are quickly flushed out .

Brief Description of the Drawings

The invention is explained below with reference to the drawing in which

Fig. 1 is a diagrammatic view of a first embodiment of an electrolytic apparatus according to the invention, an additional soluble anode being arranged in the tank,

Fig. 2 is vertical, central sectional view of the tank of Fig. 1 on a larger scale,

Fig. 3 is a plan view of the tank of Fig. 2, the upper end plate of the tank being removed,

Fig. 4 is a diagrammatic view of a second embodiment of an electrolytic apparatus according to the invention without an additional anode in the tank,

Fig. 5 is a vertical central sectional view of the tank of Fig. 4 on a larger sludge.

Fig. 6 is a plan view of the tank of Fig. 5, the upper end plate of the tank being removed,

Fig. 7 is a diagrammatic view of a modification of the electrolytic apparatus of Fig. 4, the tank being provided with a convex lower end plate,

Fig. 8 is a vertical central sectional view of the tank of Fig. 7 on a larger scale, and

Fig. 9 is a plan view of the tank of Fig. 8, the upper end plate of the tank being removed.

Best Mode for Carrying Out the Invention

The electrolytic apparatus shown in Fig. 1 is adapted for protection against corrosion of a freshwater piping system (not shown) connected to a water tank 1. The electrolytic apparatus comprises at least two electrodes 2 and 3 of aluminium arranged in the tank 1 and a control unit 4 with a source of current. The control unit 4 is adapted to step down and rectify the voltage from the source of current to a suitably low direct voltage.

The electrodes 2 and 3 are connected to the positive and negative pole of the current source through a pole changer 5 in such a manner that the electrodes 2 and 3 alternately function as anode and cathode. At a given time, the elec¬ trode 2 thus serves as anode and the electrode 3 as cathode. At the subsequent change of pole the reverse is the case, that is the electrode 2 serves as cathode and the electrode 3 as anode. In an electrolytic apparatus arranged in the above manner the electrodes 2 and 3 and the water between them may be viewed as an isolated elec- trolytic cell connected to an alternating supply of cur¬ rent. As a result, during the use of the electrolytic apparatus the calcium depositions may be restricted to a specific area, that is to the electrode, for instance 3, which serves as cathode during the time in question. When, subsequently, the polarity is reversed by means of the pole changer 5, the calcium deposits formed on the cathode 3 are loosened, whereupon they settle. They are then flushed out through an outlet valve in the bottom of the tank. Compared to the known electrolytic apparatuses, a considerable reduction of the amount of sludge and calcium present in the tank is thereby obtained. As a consequence, the bacteria are given poorer conditions of growth, result¬ ing in a lower germinal index.

Furthermore, during the operation of the electrolytic apparatus, the electrodes 2 and 3, which are of aluminium, gradually dissolve during the time in which they serve as anodes, and the dissolved aluminium forms aluminium hy¬ droxide. The aluminium hydroxide has a favourable effect in that together with liberated calcium carbonate it covers the inner surfaces of the freshwater piping system with a corrosion inhibiting layer.

Figs. 2 and 3 show the tank 1 of Fig. 1 on a larger scale and in more details. In this embodiment two substantially identical, soluble electrodes 2 and 3 of aluminium have been used. The electrodes 2 and 3 are rod-shaped, arranged diametrically opposite each other inside the tank (Fig.3) and fastened to the tank 1 in a suitable manner. More electrodes, for instance four, may however also be used. The electrodes will then have to be divided into two groups having mutually opposite polarity.

As appears from Figs. 1 - 3 at least one, that is two soluble, additional anodes 6 and 7 are arranged in the tank 1, said anodes being of aluminium, zink or a similar material and having a separate supply of current from the control unit 4. The anodes 6 and 7 are fastened to the tank 1 in a suitable manner. As the tank 1, which is assumed to be of steel or another metal, is connected to the negative pole of the current source and thus serves as cathode, the additional anodes 6 and 7 provide a cathod¬ ic protection against corrosion of the tank 1 per se.

The tank 1 of Figs. 2 and 3 is a hot water tank, which at the bottom is provided with an inlet pipe 8 for cold water and an outlet pipe for hot water at the top. In its upper portion the tank 1 is provided with a return pipe 11 for hot water which returns after having circulated in the circuit for hot water, said return pipe 11 being provided with a circulating pump 10. The water in the tank 1 is heated by water from the tank running though an outlet pipe 12, through a heat exchanger (not shown), where the water is heated and back to the tank 1 through an inlet pipe 13.

As shown in Figs. 1 and 2 the tank is provided with an upper convex end plate 14 which is provided with a vent pipe 15 with vacuum breaker. At the bottom the tank 1 is provided with a l.ower, conical end plate 16, in the lower top point of which an outlet valve 17 or sludge cock has been arranged. By means of gravitation a large amount of the precipitated calcium thereby settles in the conical top point of the end plate 16, that is just above the outlet valve 17, whereby it is easier flushed out.

As appears from Figs. 2 and 3, the tank 1 is provided with a rinsing ring 19 extending close to the skirt 18 of the tank, said rinsing ring being provided with a number of rinsing nozzles 20. At the end of the inlet pipe 8 for cold water, an upper inlet valve 21 and a lower inlet valve 22 have been inserted parallel to each other. The upper inlet valve 21 runs into the tank 1, while the lower inlet valve 22 runs into the rinsing ring 19. When the settled calcium depositions and other sludge are to be flushed out, the inlet valve 21 is closed and the inlet valve 22 is opened. Cold water is then led into the rinsing ring 19, from where the water is sprayed diagonally down towards the end plate 16 through the rinsing nozzles 20 which have been adjusted in said direction beforehand. The end plate 16 is quickly rinsed of calcium and sludge which are flushed out through the outlet valve 17. A control device 23 may be adapted to automatically shut off the valve 21, open the valve 22, stop the circulating pump 10 and open the outlet valve 17 at predetermined intervals to allow rinsing to take place.

Fig. 4 shows a second embodiment of the electrolytic apparatus , one electrode 2 or 3 further having a separate supply of current from the control unit 4. As a result, a cathodic protection against corrosion of the tank 1 per se is obtained without the use of an additional anode - cf. the anode 6 of Fig. 1 - whereby a particularly simple and inexpensive embodiment of the electrolytic apparatus is obtained.

Figs. 5 and 6 show the tank 1 of Fig. 4 on a larger scale and in greater details. The two additional anodes 6 and 7 are left out and this allows many different positions of the electrodes 2 and 3. Fig. 7 shows a modification of the electrolytic apparatus of Fig. 4, the tank 1' being provided with a convex lower end plate 16 ' .

Figs. 8 and 9 show the tank 1' of Fig. 7 on a larger scale and in greater detail. By using a convex end plate 16' instead of a conical end plate, the tank 1' is provided with less height resulting in a more compact construction.

In the above, the electrolytic apparatus is explained in connection with a hot water tank. It may, however, also be used for a cold water tank.

The electrodes 2 and 3 and the additional anodes 6 and 7 may have any suitable form and position corresponding to the given use of the electrolytic apparatus.

The apparatus is considerably less expensive if a rinsing ring 19 is not used, cf. Figs. 2,3; 5,6 and 8,9.

The tank 1 is preferably made of steel or another metal but may also be of another material, for instance plastics. If the tank is made of metal, it may have a surface layer of for instance plastics, enamel or paint on the inside.

Claims

1. Electrolytic apparatus for protection against cor¬ rosion of a freshwater piping system connected to a water tank (1;1'), said electrolytic apparatus having at least two electrodes (2, 3) which are arranged in the tank (1;1') as well as a control unit (4) with a source of current, c h a r a c t e r i s e d in that the electrodes (2, 3) are of aluminium and connected to the source of current through a pole changer (5) in such a manner that the electrodes (2,3) alternately work as anode and cathode.

2. Electrolytic apparatus as claimed in claim 1, c h a r a c t e r i s e d in that the electrodes (2, 3) are two subs antially identical, soluble electrodes.

3. Electrolytic apparatus as claimed in claim 1 or 2, c h a r a c t e r i s e d in that at least one soluble, additional anode (6, 7) is placed in the tank (1) , said anode being of aluminium, zink or a similar material and having a separate supply of current from the control unit (4).

4. Electrolytic apparatus as claimed in claim 1 or 2, c h a r a c t e r i s e d in that one electrode (2 or 3) further has a separate supply of current from the control unit (4) .

5. Electrolytic apparatus as claimed in any of the claims 1 - 4, c h a r a c t e r i s e d in that the tank

(1) is provided with a conical, lower end plate (16) , the lower top point of which is provided with an outlet valve (17) .

6. Electrolytic apparatus as claimed in any of the claims 1-4, c h a r a c t e r i s e d in that the bottom the tank (1;1') is provided with a rinsing ring (19) extending close to the skirt (18) of the tank, said rinsing ring being provided with a number of rinsing nozzles (?) (20), and that an outlet valve (17) is placed in the lower end plate (16; 16') of the tank.